The present invention relates to an apparatus for air conditioning. Particularly, the present invention pertains to an air conditioning system for vehicles and a compressor used therein.
For example, Japanese Unexamined Patent Publication No. 5-223357 discloses such a vehicle air conditioning system. The air conditioning system includes a main heater and a cooler. The main heater uses engine coolant (hot water). The cooler also functions as an auxiliary heater that uses heated gas to heat the passenger compartment. The cooler includes an external refrigerant circuit and a compressor, which is driven by a vehicle engine. The external refrigerant circuit connects a discharge chamber (discharge pressure zone) with a suction chamber (suction pressure zone), which are defined in the compressor. The external refrigerant circuit includes a condenser, an expansion valve and an evaporator, which are arranged sequentially from the discharge pressure zone to the suction pressure zone. The discharge pressure zone of the compressor is also connected with the evaporator by a bypass, which bypasses the condenser and the expansion valve. A decompression device is located in the bypass. The passage between the discharge pressure zone and the suction pressure zone is switched by a switch valve. Specifically, the switch valve switches between a route including the condenser and the expansion valve and a route including the bypass, which bypasses the condenser and the expansion valve.
When the engine is started, the temperature of the coolant is low. Therefore, the main heater is unable to supply warm air to the passenger compartment. When the temperature of the coolant is low, the cooler is controlled to function as an auxiliary heater. Specifically, the switch valve selects the route that bypasses the condenser and the expansion valve. Then, high pressure, high temperature refrigerant gas discharged from the compressor is provided to the evaporator via the bypass and the decompression device. The heat of the gas is transferred by the evaporator. The heat of the refrigerant gas is added to the heat produced by the main heater, which allows the air conditioning system to quickly send warm air to the passenger compartment.
A typical prior art air conditioning system includes a variable displacement compressor 60 illustrated in FIG. 6. A suction chamber 61, a discharge chamber 62 and a crank chamber 63 are defined in the compressor 60. Cylinder bores 64 are formed in a cylinder block 65. Each cylinder bore 64 houses a piston 66. A drive shaft 67 is rotatably supported by the compressor housing. The drive shaft 67 is driven by a vehicle engine 68. A swash plate 69 is supported by the drive shaft 67 in the crank chamber 63 to be tiltable relative to the drive shaft 67. The pistons 66 are engaged with the swash plate 69. A supply passage 70 communicates the discharge chamber 62 with the crank chamber 63. A bleeding passage 71 communicates the crank chamber 63 with the suction chamber 61. A control valve 72 is located in the supply passage 70.
Rotation of the drive shaft 67 is converted to linear reciprocation of each piston 66 by the swash plate 69. Reciprocation of each piston 66 draws refrigerant gas from the suction chamber 61 to the associated cylinder bore 64. The gas is then compressed and discharged to the discharge chamber 62. The control valve 72 adjusts the flow rate of gas in the supply passage 70 thereby varying the pressure of the crank chamber 63. This changes the difference between the pressure of the crank chamber 63 and the pressure of the cylinder bores 64. Accordingly, the inclination of the swash plate 69 is changed.
When the control valve 72 opens the supply passage 70, highly pressurized gas in the discharge chamber 62 is supplied to the crank chamber 63, which increases the pressure of the crank chamber 63. The difference between the pressure of the crank chamber 63 and the pressure in the cylinder bores 64 decreases the inclination of the swash plate 69. This shortens the stroke of each piston and decreases the displacement of the compressor 60.
When the control valve 72 closes the supply passage 70, highly pressurized gas in the discharge chamber 62 is not supplied to the crank chamber 63. Since the crank chamber 63 is connected to the suction chamber 61, the pressure of which is relatively low, by the bleeding passage 71, the pressure of the crank chamber 63 is lowered. Then, the pressure of the cylinder bores 64 moves the swash plate 69 to increase the inclination of the swash plate 69. This lengthens the stroke of each piston 66 and increases the displacement of the compressor 60.
The compressor 60 has a spring 73 to urge the swash plate 69 in a direction decreasing the inclination. When the compressor 60 is stopped, the spring 73 moves the swash plate 69 to minimize the inclination. When the compressor 60 is started again, the displacement of the compressor 60 is minimum, which requires minimum torque. The shock caused by starting the compressor is thus reduced. If the nonoperational state of the compressor continues, the pressures in the chambers of the compressor 60 become equalized at a relatively low pressure. Therefore, when the compressor 60 is started again, it takes a relatively long time to maximize the cooling performance or the heating performance in the auxiliary heater. That is, the pressure in the discharge chamber 62 is increased slowly and it takes a relatively long time for the swash plate 69 to move from the minimum displacement position to the maximum displacement position. The compressor in the prior art air conditioning system is therefore slow to start functioning to cool the passenger compartment and slow to work as an auxiliary heater. When the temperature about the evaporator is low, the evaporator transfers a significant amount of heat from the gas. In other words, the work of the evaporator is increased. Therefore, the evaporator greatly lowers the pressure of the gas. In this case, it takes even longer time to increase the pressure of the discharge chamber 62. That is, it takes a relatively long time for the compressor 60 to start functioning as the auxiliary heater.